1. Field of the Invention
The present invention relates to a height adjusting device for an automotive seat, and in particular relates to an improvement of such type of height adjusting device wherein the forward and rearward parts of seat back of the seat are adjustable in height independently of each other.
2. Description of prior Art
As typically shown in FIG. 1, an ordinary, hitherto height adjusting device, of this kind, by which the forward and rearward parts of seat back of the seat are adjusted in height, independently of each other, is formed with an upstanding bracket (102) erected upon a slide rail (101), wherein a forward torque shaft (103) and rearward torque shaft (104) are rotatably mounted at the the bracket (102). Although not shown, the slide rail (101) and bracket (102) are each provided as two spaced-apart components, and thus a pair of brackets (102) are respectively mounted on a pair of slide rails (101), with the two torque shafts (103)(104) extended between the brackets. A first sector gear (107) is fixed to the forward torque shaft (104) and meshed with a pinion (109) fixed on an operation spindle (110). To the first sector gear (107), is pivotally connected the lower end of a forward link member (106) which is at its upper end pivotally connected to a frame (not shown) of a seat cushion (118). A first operation handle (112) is fixed on the spindle (110) which is supported through the bracket (102) rotatably. Thus, rotation of the handle (112) causes the vertical movements of the forward part of the seat cushion (118). On the other hand, to the rearward torque shaft (104), is fixed a L-shaped rearward link member (105) whose lower end is connected via a connecting rod (117) with a movable plate (108) mounted rotatably on the bracket (102), the movable plate (108) having a sector gear portion which is meshed with a pinion (113) fixed on an operation spindle (114). The upper end of the rearward link member (105) is pivotally connected to a frame (not shown) of the seat cushion (118). A second operation handle (116) is fixed on the spindle (114) which is rotatably supported through the bracket (102). With this structure, like the first handle (102), rotation of the second one (116) causes the vertical movements of the rearward part of the seat cushion (118). Designations (111)(113) denote a first non-reversible brake device and a second non-reversible brake device, respectively, which are adapted to prevent the reverse rotation of both operation spindles (110)(114), so as to serve to retain a height of both forward and rearward parts of the seat cushion (118). This structure is found commonly from the Japanese Laid-Open Patent Publication No. 61-200040, for example.
However, in the above-constructed prior art height adjusting device, an undesired idle, rattling problem exists in the linkage mechanism at the rearward part thereof. Certainly, the forward linkage, namely, the sector gear (107) and forward link member (106), is directly retained by the first non-reversible brake device (111) against rattling or wobbling, but by contrast, the rearward linkage, namely, the rearward link member (103), connecting rod (105), and movable plate (108), is given a play due to the presence of the connecting rod (117) between the rearward link member (103) and movable plate (108), which results in a rattling or wobbling in such linkage. Consequently, the prior art has been with a rattling problem in the rearward part of the seat cushion.